In a conventional air brake system the braking force is obtained by supplying pressurized air to the brake cylinder at one side of the piston therein. The brake is released by discharging the air from the cylinder, the air thus being lost.
In a known modification of this brake the braking force is obtained by means of a very heavy pretensioned spring, which acts on one side of the piston, the brake being released by the supply of pressurized air on the opposite sides of the piston. When the brake is to be applied again, also in this case air has to be discharged and will be lost.